This disclosure relates generally to refrigeration systems having a compressor powered by a fuel-fired engine. More particularly, this disclosure relates to calibration of an engine throttle position sensor during operation of a fuel fired engine of a transport refrigeration system.
Fruits, vegetables and other perishable items, including meat, poultry and fish, fresh or frozen, are commonly transported in the cargo box of a truck, a trailer, or in an intermodal container. Accordingly, it is customarily to provide a transport refrigeration system in operative association with the cargo box for cooling the atmosphere within the cargo box. The transport refrigeration system includes a refrigerant vapor compression system, also referred to as a transport refrigeration unit, and an on-board power unit. The refrigerant vapor compression system typically includes a compressor, a condenser, an expansion device and an evaporator serially connected by refrigerant lines in a closed refrigerant circuit in accord with known refrigerant vapor compression cycles. The power unit includes a fuel-fired engine, typically diesel fueled.
In many truck/trailer transport refrigeration systems, the compressor of the transport refrigeration unit is driven by the engine shaft either through a belt drive or by mechanical shaft-to-shaft link. More recently, all electric transport refrigeration systems have been developed for truck/trailer applications wherein the engine drives an on-board generator for generating sufficient electrical power to drive an electric motor operatively associated with the compressor of the transport refrigeration unit. For example, U.S. Pat. No. 6,223,546, assigned to Carrier Corporation, the same assignee to which this application is subject to assignment, the entire disclosure of which is incorporated herein by reference in its entirety, discloses an electrically powered transport refrigeration unit powered by an engine driven synchronous generator capable of producing sufficient power to operate the compressor drive motor and at least one fan motor. With respect to intermodal containers, clip-on power units, commonly referred to as generator sets or gensets, are available for mounting to the intermodal container, typically when the container is being transported by road or rail, to provide electrical power for operating the compressor drive motor of the transport refrigeration unit associated with the container. The genset includes a diesel engine and a generator driven by the diesel engine.
In conventional transport refrigeration systems, the control system is open loop in that the refrigeration system controller is unaware of the actual operating engine load. The fuel-fired engine is controlled by an electronic engine controller independently of the transport refrigeration unit which is controlled by a dedicated refrigeration unit controller. The electronic engine controller controls fuel flow to the engine so as to maintain the engine speed at a target RPM irrespective of the load imposed on the engine by the refrigeration unit. The refrigeration unit controller is unaware of the actual load being imposed on the engine and controls the refrigerant unit to meet cooling demand irrespective of the actual load on the engine.